1. Field of the Invention
This invention relates to a detector for measuring torque on a shaft, and in particular to a torque detector using magnetostriction.
2. Description of the Prior Art
Ferromagnetic materials exhibit magnetostriction. In a process of magnetostriction, when the ferromagnetic material is subjected to mechanical stress, magnetic properties of the material vary.
It is known to use magnetostriction in order to determine torque on a shaft.
Japanese patent publication 51-60580 discloses such a torque detector. In this detector, a shaft connecting a mechanical power source and a load is coated with a film of magnetic material. Torque on the shaft distorts the shaft, varying magnetic properties of the magnetic film. This magnetic variation is measured via a sensor including a pair of exciting coils and a pair of sensing coils disposed near the magnetic film and are electromagnetically coupled to each other via the magnetic film. When an alternating current flows through the exciting coils, an electrical signal induced across the sensing coils depends on the magnetic properties of the film and thus represents the torque on the shaft.
This torque detector includes a zero-adjusting arrangement to make its output zero when no torque is applied to the shaft. The zero-adjuster appears excessively sensitive, so that it seems not easy to handle the adjuster.